The French Nuclear Safety Authority, ASN, said it was not clear what caused the fires but firefighters had found small pools of burning oil and had quickly extinguished the flames.
The crisis situation put in place on Thursday evening has been lifted and the authority hopes to inspect the site on Friday.
EDF, which operates the plant, said the installation was secure, no one was injured and there were “no consequences for the environment.”
But Cecile Duflot, of the Frane's Green party, EELV, described the incident as “very serious” and said overall there was a lack of transparency on the nuclear issue in France.
“We are always being told: it’s not serious, it’s not serious, it is never serious,” she said. “I think, in the light of the information we have been given, that it is a very serious incident, but it is not a catastrophe.”
France generates 75 percent of its electricity from nuclear power and the future of the industry has become an issue in campaigns for the presidential election to be held in April and May.
France, the world's most nuclear-dependent country, operates 58 reactors and has been a leading international proponent of atomic energy.
But the country's reliance on nuclear power has been called into question since the Fukushima disaster in Japan, which prompted Germany to announce plans to shut all of its reactors by the end of 2022.